Yes, the yellowing is caused on Bbags (post 2004) with glazing on the leather. The yellowing affect is caused by the UV rays oxidising the glaze. Actually, all glazed bags, when left in the sun / hot cars do gradually turn yellow. You can only notice it more on light bags. The best prevention is to buy a conditioning and polishing product that is gentle enough to use on a regular basis. You need to create a film of protection (not necessarily SPF protection) between your glaze and the natural elements. If you don't want a yucky boot-polish smell lingering, you can use a fragrance-free or lightly scented conditioner and polish that don't contain petro-chemicals. You can really feel and smell the difference!